Abstract The Zero Emissions Research and Technology (ZERT) project at the Los Alamos National Laboratory is studying the injection of CO 2 into geologic repositories. We are formulating the problem as science based decision framework that can address issues of risk, cost, and technical requirements at all stages of the sequestration process. The framework is implemented in a system model that is capable of performing stochastic simulations to address uncertainty in different geologic sequestration scenarios, including injection into poorly characterized brine aquifers. Processes level laboratory experiments, field experiments, modeling, economic data, and risk theory are used to support the system level model that will be the basis for decision making. The current system model, CO2-PENS, is already proving to be useful in showing complex interactions between the different components of the framework. The system model also provides a consistent platform to document decisions made during the site selection, implementation, and closure periods. CO2-PENS: A CO 2 Sequestration Systems Model Supporting Risk-Based Decisions Philip H. Stauffer, Hari S. Viswanathan, George D. Guthrie, Rajesh J. Pawar, John P. Kaszuba, James W. Carey, Peter C. Lichtner, Chuan Lu, Ionnis N. Tsimpanogiannis, Hans J. Ziock, Manvendra K. Dubey, Seth C. Olsen, Steve J. Chipera, Julianna E. Fessenden 2) CO 2 -PENS System Level Model used to explore complex interactions between Risk, Cost, and Technical Requirements 3) Process Level Investigations used to Support System Level Calculations 1)A Science-Based Decision Framework for P redicting E ngineered N atural S ystems Nordbotten, J, M. Celia, S. Bachu, Water Resources Research, Core Flood Experiment Calcite dissolution Numerical Modeling using LANL Porous Flow Codes FEHM and PFLOTRAN Output concentration 10 m above an injection site Analytical Solutions for Wellbore Failure Obtain leakage rates using semi-analytical solutions, collaboration with M. Celia and others at Princeton Reaction zone SACROC Core Analysis Cement 3cm CO2 Mineralization : Dawsonite Synthesis Experiments Reservoir Processes >> CO 2 Fate and Transport Cement Degradation >> Wellbore failure CO2 Cement Brine Experiment pH sensitive dye Ca(OH)2 (high pH) -> CaCO3 (low pH) PCO2 = 13.8 MPa CO 2 mass in the reservoir and various leakage pathways Borehole failure and repair information FLOTRAN reactive chemistry simulations Main Simulation Control Reservoir Variables Input CO2 - PENS Model Root The model root is based on the conceptual framework. The system model is designed to adapt to changes in understanding and can be modified quickly to add new processes and interactions. Identification of additional processes and interactions can come through use of the system model, literature searches, and through independent investigations undertaken to support the decision making process. The model root, created in GoldSim, is used to manage global variables such as time, CO 2 mass balance, total risk, well statistics, and costs. GoldSim is also used to sample stochastic distributions and allows robust uncertainty analysis. Subprograms, written in the language of choice (i.e., FORTRAN, C) are called from the model root. These subprograms can be changed to include more detailed calculations as data and theory are revised. Multiple options for subprograms allow flexibility. For example, limited availability of data may obviate the need for a complex subprogram. Example Output 30 yr in-situ CO 2 exposure history retrieved from core near the reservoir/caprock interface. SACROC, Texas Special Thanks for providing the core to: LAUR Unclassified Significant Clay Growth Occurs Hobbs Injection Site Field injection Lab experiments Numerical simulations CO2 - PENS Conceptual Framework Multiphase flow; Water -CO 2 - Air: Fractured porous media: Reactive chemistry: Thermal effects: Density driven flow: Supercritical CO 2 : PFLOTRAN is now massively parallel  Multiple layers  Reduced complexity relative to FEHM simulations  Couple analytical solutions to the CO 2 -PENS system model 8000 yrs Mole fraction dissolved CO2 Numerical simulation using FLOTRAN Visualization of Wormhole formation Data Analysis by New Mexico Tech Image by UC Davis 0.2 m x 0.2 m (m) pH (m) Risk Analysis